1. Technical Field
This invention relates generally to sensing devices for detecting movement of ferrous elements, such as rolling elements in linear and rotational motion devices and gear teeth in gear trains.
2. Related Art
Linear motion assemblies, such as lead screws, linear rail and carriage assemblies, and ball screws, and rotational motion assemblies, such as bearings and gear trains, are used in a numerous industries, such as the machine tool, automotive, aircraft and aerospace industries, to effect linear or rotational movement of one body relative to another body. Typically, these assemblies are constructed to have life spans approximating their projected period of use. A ball screw assembly, for example, has a life span that is generally expressed as a function of the number of inch cycles that either the ball screw and/or ball nut will travel under a given load and at a given rotational speed. As such, when a ball screw assembly or any of the other of the assemblies mentioned above for effecting relative movement is in use, a routine maintenance schedule is generally adopted calling for periodic inspections to determine whether the respective assemblies are functioning properly. Though routine maintenance schedules can prove beneficial in making use of more of the full useful life of the respective assemblies, such schedules do not permit an unforeseen problem to be detected as the problem is developing in real-time. As such, some of the potentially useful life of the respective assemblies may be unused when replaced, according to schedule, in advance of any unacceptable deterioration. Also, deterioration that occurs in advance of the estimated useful life of assemblies may go undetected until failure occurs.